A yellow ABS malfunction lamp on the trailer (typically left side) means:
Correct. A trailer-mounted yellow ABS lamp indicates the trailer's ABS is malfunctioning. Service brakes still work; have the system repaired.
CDL Practice Question #145
Category: Air Brakes
Why this question matters
This question is one of 71 in our Air Brakes bank. The reasoning above comes directly from the AAMVA CDL Manual, the source document used by every U.S. state DMV. Memorizing the underlying rule — not just the letter answer — is what separates passing on the first attempt from a return trip and another fee.